code: def sampling_systematic(n):
      """
      Return a subset where items are selected at a regular interval.
  
      Parameters
      ----------
      n : int
          Number of items to return.
  
      Returns
      -------
      `FeatureSpec`
          Systematic sample specification.
  
      Examples
      --------
      .. jupyter-execute::
          :linenos:
          :emphasize-lines: 9
  
          import numpy as np
          from lets_plot import *
          LetsPlot.setup_html()
          n = 1000
          x = np.arange(n)
          np.random.seed(12)
          y = np.random.normal(0, 1, n)
          ggplot({'x': x, 'y': y}, aes(x='x', y='y')) + \\
              geom_line(sampling=sampling_systematic(50))
  
      """
  
      return _sampling("systematic", n=n)
  
file_path: lets-plot/python-package/lets_plot/plot/sampling.py
imports: from .core import FeatureSpec
label_desc: Use image node_id 4 for calling a global function with example usage: sampling_systematic(n) and returns: _sampling